1. Field of the Invention
2. Description of the Related Art
As shown in FIG. 5, in a conventional air impact wrench, a cylindrical reverse apparatus R5 is disposed between a trigger 59 and an impact wrench main body 51 and in parallel with an output shaft of an air motor. The reverse apparatus R5 includes a reverse bush fitted to the main body 51 and a reverse valve slidably inserted into the reverse bush.
In the conventional air impact wrench, when the direction of rotation of the air motor is to be changed from clockwise (forward) to counterclockwise (reverse), an operator pushes an end of the reverse apparatus R5 on an end cap 53 side by use of the thumb of the hand that grasps a grip 57, such that an end of the reverse apparatus R5 on an anvil 56 side projects. When the direction of rotation of the air motor is to be changed from counterclockwise (reverse) to clockwise (forward), the operator pushes the end of the reverse apparatus R5 on the anvil 56 side by use of the forefinger of the hand such that the end of the reverse apparatus R5 on the end cap 53 side projects.
As described above, the conventional reverse apparatus requires operation by use of two fingers (thumb and forefinger) of the hand that grasps the grip. In the case of a type of work, such as automobile maintenance and repair work, which must be performed in a narrow work space and in which the direction of rotation of the air impact wrench must be switched frequently, work efficiency tends to decrease.
In view of the foregoing, an object of the present invention is to provide a reverse apparatus for an air impact wrench which enables an operator to switch the direction of rotation by use of a single finger of the hand that grasps a grip of the air impact wrench.
In order to achieve the above object, the present invention provides a reverse apparatus for an air impact wrench in which pressurized air supplied to an air supply passage provided within a grip is fed via the reverse apparatus to an air motor accommodated within an impact wrench main body, and rotational torque output from the air motor is transmitted to an anvil via an impact mechanism, comprising a cylindrical bush disposed in a lower portion of the impact wrench main body substantially in parallel with an output shaft of the air motor; a valve member slidably disposed within the bush and having an end projecting from the lower portion of the impact wrench main body, the valve member cooperating with the bush in order to supply pressurized air to one of two air ports of the air motor, when positioned at a first axial position, so as to rotate the anvil clockwise and supply pressurized air to the other air port of the air motor, when positioned at a second axial position, so as to rotate the anvil counterclockwise; and a cam mechanism disposed within the bush and operatively coupled to the valve member so as to position the valve member to the first and second axial positions alternately whenever the projecting end of the valve member is pushed inward.
Preferably, the cam mechanism comprises a circumferentially extending cam provided on an inner circumferential surface of the bush, the cam having a plurality of axially extending grooves circumferentially arranged at a predetermined pitch and circumferentially extending engagement surfaces each formed between corresponding two of the grooves; a spring support attached to one end of the bush; a first spring attached to the spring support; a spin ring rotatably disposed within the bush and having a plurality of convex portions formed on a circumferential surface thereof, the convex portions being caused to enter the grooves or run onto the engagement surfaces between the grooves; a cam roll rotatably disposed within the bush and having at an axial end thereof a cam surface to be engaged with the convex portions of the spin ring, the cam surface having a profile such that each time the cam roll is moved axially, the spin ring is rotated by an angle corresponding to half the pitch of the grooves; and a second spring disposed within the bush and adapted to maintain mutual contact among the spin ring, the cam roll, and the valve member, the second spring generating force being smaller than that generated by the first spring.
Preferably, the bush has an air inlet port communicating with the air supply passage and first and second air feed ports communicating with the air ports of the air motor, the air feed ports being located on opposite sides of the air inlet port with respect to the axial direction; and the valve member has a changeover portion having a diameter substantially equal to an inner diameter of the bush, the changeover portion moving to a position between the first air feed port and the air inlet port when the valve member is moved to the first axial position and moving to a position between the air inlet port and the second air feed port when the valve member is moved to the second axial position.
More preferably, a regulation lever is attached to the projecting end of the valve member; and the valve member has an opening control portion formed adjacent to the changeover portion for controlling the opening of the air inlet port when the valve member is rotated upon rotation of the regulation lever.